In recent years, requirements for a reduced fuel consumption in automobiles have become increasingly severe from a viewpoint of economy of resources or protection of the environment. Thus, rubber materials for tires having improved rolling resistance and abrasion resistance are eagerly desired. It is known that rolling resistance can be improved by incorporation of silica as a reinforcer in rubber, but the incorporation of a silica reinforcer enhances abrasion resistance and tensile properties to a smaller extent than that obtained by the incorporation of carbon black as a reinforcer in rubber.
A primary cause of this phenomenon is to be sought in the fact that, as compared with carbon black, silica has a poor affinity for rubber materials and exhibits a poor reinforcing effect thereon. A proposal of using a silane coupling agent has been made for enhancing the affinity of silica for rubber materials, for example, in Japanese Unexamined Patent Publication (JP-A) No. H3-252431 and JP-A H3-252433. This proposal has a problem such that the silane coupling agent is expensive and must be used in a large amount.
For enhancing the affinity of silica for rubber materials without the use of a silane coupling agent, another proposal of introduce into rubber materials a substitution group having a good affinity for silica, For example, the incorporation of an alkylsilano group (JP-A H1-188501), an alkoxysilano group (JP-A H5-230286) or a substituted amino group by the reaction of 4,4'-bis (diethylamino) benzophenone (JP-A S64-22940) in a diene polymer rubber by an anion polymerization has been proposed, and the incorporation of a tertiary amino group in a diene polymer rubber by an emulsion polymerization has been proposed in JP-A H1-101344. However, even though these modified rubber materials are used, the modified rubber compositions still do not have a good rolling resistance, and, as compared with carbon black-incorporated rubber compositions, the modified rubber compositions do not have good and balanced tensile stress and abrasion resistance.
It also has been proposed provide a primary amino group in a diene copolymer rubber. For example, the reaction of an anion polymer having an active lithium metal with an N-unsubstituted aziridine is described in U.S. Pat. No. 3,801,520; the reaction of an anion polymer with a cyclic hydrazine compound, followed by a ring-opening with hot concentrated hydrochloric acid, is described in JP-A S62-34904; and the reaction of an anion polymer with a bifunctional Schiff base compound, followed by hydrolysis under an acidic condition, is described in JP-A S 62-265305. However, these proposed techniques are concerned with the provision of modified polymer rubbers for modifying molding resin materials, and are completely silent on the use and characteristics thereof other than those as the modifiers for molding resin materials.